Magnet valve, in particular for fuel injection pumps

ABSTRACT

A magnet valve that serves to block off a fuel intake line to control fuel flow to supply a pump work chamber of a fuel injection pump with fuel, a closing element has a bore entering at the face end, which bore can be closed by a valve member under the influence of a closing spring. When pressure surges occur in one part of the intake line which is closed by the closing element and leading to the pump work chamber, instead of the closing element and the entire cross section of the intake line portion being opened, only the cross section of the bore is opened. Once it has been pushed open, this bore is rapidly closed again by the low-mass valve member, so that only small quantities of fuel can flow via the bore for pressure equalization.

BACKGROUND OF THE INVENTION

The invention is based on a magnet valve as defined hereinafter. In sucha magnet valve, known from German Patent 25 03 345, the closing elementis coupled to the armature of the magnet valve via a drag coupling, andthe armature is embodied with its face end that plunges into the closingpart as a valve element, so that this element blocks the communicationbetween the intake line parts via the bore whenever the armature, underthe influence of the restoring spring, moves or has moved the closingpart into the closing position. Upon opening of the magnet valve thearmature is lifted from its seat on the closing part under the influenceof the magnetic force of the electromagnet, opens the bore, and only inthe course of a further stroke lifts the closing part from its seat viathe drag coupling, so that the force for opening the closing part, whichis acted upon by both the restoring spring and the pressure prevailingupstream of the seat in the intake line, can be kept small, because apressure equalization is effected previously via the bore.

Under certain conditions, however, it may happen with a magnet valve ofthis generic type that the closing part, when it is moved to the closingposition, is acted upon by a pressure pulse from the pump work chamberin the course of the remaining delivery stroke of the fuel injectionpump and after opening of the communication between the intake line andthe pump work chamber. This pressure pulse can cause the closing part tobe lifted from its seat, so that a process of refilling the pump workchamber can briefly take place via the intake line. This quantityflowing through the pump work chamber can also be brought to injectionin the next delivery stroke of the pump piston, and thus the purpose ofthe magnet valve, which is to serve for the purpose of shutoff, is notattained. In particular, with such a defect in the control of the fuelinjection pump, the internal combustion engine can race.

ADVANTAGES OF THE INVENTION

A magnet valve according to the invention has the advantage over theprior art that pushing open of the closing part and thus acorrespondingly large flow of fuel to the pump work chamber isprevented, since the pressure pulse is reduced via the open valvemember, which opens only a small overflow cross section.

By the provisions recited in the specification further advantageousdevelopments of and improvements will become apparent. A small valvemember with flow mass is the result which can reach its closing positionagain with low inertia, so that there is only a minimal reverse floweffect after the valve member has been pushed open. The disadvantagesreferred to at the outset are thus avoided to the greatest possibleextent.

DRAWINGS

One exemplary embodiment of the invention is shown in the drawing, andwill be described in further detail in the ensuing description.

FIG. 1 is a fragmentary longitudinal section through a fuel injectionpump, in which magnet valve according to the invention is used;

FIG. 2 is a fragmentary section through FIG. 1 along the line II--II;and

FIG. 3 is a longitudinal section through the magnet valve according tothe invention, on a larger scale.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

In the fuel injection pump shown in FIG. 1 for multi-cylinder internalcombustion engines, a cylinder liner 2 is inserted into a housing 1, andin its cylinder bore 3, a pump piston 4 is set into simultaneouslyreciprocating and rotating motion, as indicated by the arrows in thedrawing, by a drive mechanism and cam drive, not further shown, of thefuel injection pump. In the cylinder bore 3, the pump piston 4 on itsface end encloses a pump work chamber 6, which is supplied with fuel inthe intake stroke of the pump piston via longitudinal grooves 8, whichserve as filling grooves, originating at the face end 7 of the pumppiston. As can be seen from FIG. 2, which is a section through FIG. 1along the line II--II, the filling grooves 8 are distributed at uniformangular intervals around the jacket face of the pump piston. In FIG. 2,four of these grooves are shown, corresponding to four intake strokeseffected per pump piston revolution, for supplying in this case fourinjection nozzles in alternation through this distributor fuel injectionpump. During the intake stroke, one of the filling grooves 8 at a timeis made to communicate with an intake line 10 discharging laterally intothe cylinder bore 3, this line communicating with a pump suction chamber11, which is enclosed in the housing of the fuel injection pump. Thepump suction chamber 11 is supplied with fuel, which is preferably atrpm-dependent pressure, by a fuel feed pump 12 from a fuel supply tank14, under the additional control of a pressure control valve 15 that islocated parallel to the fuel feed pump 12, which is driven synchronouslywith the fuel injection pump in terms of rpm.

The end of the pump piston opposite the pump work chamber 6 protrudesinto the aforementioned pump suction chamber 11, where it is connectedto the drive mechanism, not shown. Inside the suction chamber, anannular slide 17 is displaceably disposed on the jacket face of the pumppiston; this slide is displaceable in a known manner via a governor of aknown type, not shown here, via a governor lever 18 and in this processcontrols the outlet opening of a transverse bore 19 in the pump piston.The transverse bore 19 communicates with the longitudinal conduit 20 inthe pump piston, which enters axially at the face end 7 of the pumppiston and ends as a blind bore. Also branching off from thislongitudinal conduit is a radial bore 21, which leads to a distributoropening, in this case a distributor groove 22, on the jacket face of thepump piston. Injection lines 23, which for example each lead via apressure valve to one injection valve 25, branch off from the cylinderbore 3 at the level of this distributor groove. Such injection lines aredistributed about the circumference of the cylinder bore 3 in a numbercorresponding to that of the injection valves to be supplied, in thiscase four, as a result of the fact that the pump piston executes fourdelivery strokes per revolution.

During the various intake strokes of the pump piston, the pistonaspirates fuel from the pump suction chamber 11 via the filling groove8, which then has been made to coincide with the intake line, so thatthe pump work chamber 6 is filled with fuel when the ensuing deliverystroke begins. In the load position, the annular slide 17 has thenclosed the outlets of the transverse bore 19, so that in the ensuingdelivery stroke of the pump piston and after reclosure of the fillinggroove in the pump work chamber, the fuel is brought to high pressure,and then via the longitudinal conduit 20 and one of the injection lines23 is supplied to the corresponding fuel injection valve and isinjected. To end the high-pressure injection, the transverse boreemerges from coincidence at a stroke predetermined by the annular slide17, so that the pump work chamber is now relieved toward the pumpsuction chamber, via the longitudinal bore 20 and the transverse bore19, the feed pressure of the pump piston drops below the openingpressure of the injection valve, and the high-pressure injection is thusinterrupted.

For turning off the engine or to terminate the high-pressure injection,a magnet valve 27 is also provided in the intake line 10, and itsclosing element 28 cooperates with a valve seat 29 embodied as a flatseat, on which the closing element 28 comes to rest by the force of arestoring spring when the magnet of the magnet valve is without current.The valve seat is located at the transition between a stepped boreportion 31 of small diameter, toward the pump chamber, and the steppedbore portion 30 of large diameter of a stepped bore, which receives themagnet valve inserted from the outside. From the stepped bore portion 30of large diameter, the intake line 10 leads on to the pump suctionchamber 11. The stepped bore portion 31 of small diameter dischargesinto a recess 32 in the cylinder liner 2, and from there an intake linesegment 33 of rectangular cross section discharges into the cylinderbore 3.

The magnet valve 27 is shown in detail in FIG. 3. A magnet coil 39 and aguide sleeve 40 surrounded by it, into which a magnet core 41 plunges,are disposed in the housing 38 of the magnet valve. An armature 42,which is loaded by the restoring spring 43, is displaceable in the guidesleeve 40. On the side of the magnet valve remote from the armature, thevalve housing 38 is closed by a plastic part 44, through which thecurrent supply line 45 leads to the magnet coil 39. The space existingbetween the valve housing 38 and the magnet coil 39 is filled with asynthetic resin, to prevent valve parts from jarring loose because ofshocks transmitted from the engine. The core 41 and the armature 42 areconically embodied on the face ends oriented toward one another, inorder to obtain a favorable magnetic force transmission when the strokesnecessary for the use of the magnet valve are long. The armaturesimultaneously acts as a valve element, in that its end protruding fromthe guide sleeve 40 into the stepped bore portion 30 of larger diameteris embodied as a closing element 28. To this end, a hat-shaped cap 47 ofelastic sealing material is vulcanized onto this end of the armature 42and comes to rest on the face end of the valve seat 29 with itsencompassing outer edge 48 whenever the armature and closing element 28are brought into the closing position by the force of the restoringspring 43 when the magnet coil is without current.

The armature 42 has a bore 50 passing through the face end of the cap 47coaxially with the stepped bore portion 31; and the bore 50 dischargesinto the receiving bore 53 of larger diameter via a conical valve seat52, which may instead be spherical. This receiving bore is continuedwith substantially the same diameter as far as its outlet at theconically shaped face end of the armature opposite the core 41. Therestoring spring 43 is disposed in this receiving bore and is supportedon the face end on the correspondingly conically embodied core, on ashoulder portion, and at the other end is supported on a sleeve which ispressed into the receiving bore 53. This sleeve, which may instead befixed in the receiving bore in some other way, can be called anintermediate spring plate 55, because a closing spring 57 is supportedon it on the other end. This spring 57, which is embodied as acompression spring, comes to rest with its other end on a spring plate58, which is displaceable inside the receiving bore 53. On its face endtoward the bore 50, the spring plate has a recess 60, in which a ball 61that serves as a valve element is centered. On the other hand, in theclosing position, the ball 61 comes to rest on the conical valve seat 52which is provided between the receiving bore 53 and the bore 50.Advantageously, the spring plate 58 is of plastic and has a stem 63 onthe side with the closing spring 57; the stem protrudes through a middleopening 64 in the intermediate spring plate 55 and is guided therein. Onits circumference, the intermediate spring plate 55 has recesses 67, sothat upon an adjustment of the intermediate spring plate or of thearmature, fuel can flow unthrottled past the intermediate spring plate,and its motion is unhindered. Branching off from the receiving bore 53are transverse openings 66, by way of which the parts of the intake line10 upstream and downstream of the valve seat 29 are in communication,when the valve member 61 is lifted, even if the closing element 28 is inthe closing position, and upon opening of the closing element 28 by thearmature 42, the fuel positively displaced by the armature can flow outby way of this contruetion.

The low mass of the ball 61 and spring plate 58 with a correspondinglydimensioned closing spring enables a very fast opening and reclosure ofthe bore 50 or of the communication between the intake line parts withlow hysteresis. In this way the flow of relatively large quantities offuel from the pump work chamber for pressure equalization is prevented,even if the valve member had been moved into the opening position bypressure surges. The lifting from its seat of the valve element 28 thatcontrols the essentially greater diameter of the stepped bore portion 31is prevented in each case.

The danger of engine racing is thus reduced. The danger of engine racingexists particularly whenever the annular slide 17 has been displaced toa very high position toward the pump work chamber and has for instancebecomes jammed, so that the entire or nearly entire quantity of fuelthat can be fed by the pump piston leaves the work chamber and isinjected, since only a very small residual stroke or none at all, withrelief toward the pump suction chamber, now takes place. The danger alsoexists whenever, because of the injection timing adjustments, thedelivery stroke of the pump piston is late with respect to itsrotational position, so that the filling grooves 8 already furnish thecommunication between the pump work chamber and the intake line 10 or31, 32, 33 at top dead center of the pump piston or earlier. As aresult, fuel at high pressure suddenly enters the recess 32 and theadjoining stepped bore portion of smaller diameter 31, and this fuelacts in a pulselike fashion on the closing element 28 and attempts tolift it. Because of the storage capacity of the elastic fuel medium, arelatively larger quantity of fuel can therefore be stored in the spacebetween the cylinder bore 3 of the valve seat 29, especially if negativepressures are again compensated for via the intake line 10 with theclosing element 28 opened. This stored quantity flows to the pump workchamber in the ensuing intake stroke, and the pressure of the fuel inthe recess 32 and adjoining areas 31, 33 and in the pump work chamber islowered accordingly. After the closure of the portion 33 of the intakeline by the filling groove, a volume of relatively low pressure remainsin the region up to the valve seat, and a majority of the fuelpreviously stored there at high pressure has reached the pump workchamber. From it, the fuel can again be injected upon the ensuingcompression stroke, particularly if the pump work chamber cannot berelieved via the annular slide. At the end of the delivery stroke, uponreopening of the portion 33 of the intake line, or of the followingspaces, the pressure search can again push open the closing element 28,which is followed by a pressure equilibrium and a renewed inflow of fuelto the pump work chamber as described before. With the embodimentaccording to the invention, these processes are now maximally avoided.As a result, reliable shutoff of fuel injection is attained.

The foregoing relates to a preferred exemplary embodiment of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

We claim:
 1. A magnet valve for controlling a fuel supply to injectionpumps for supplying fuel to internal combustion engines, which comprisesan intake line (10) that connects a pump work chamber (6) of the fuelinjection pump to a fuel supply source (11), said magnet valve ispositioned relative to said intake line (10) to block fuel flow tocontrol an end of the fuel injection and to permit fuel through saidintake line (10) said pump work chamber during an intake stroke of apump piston (4); said magnet valve includes a closing element (28)connected to an armature (42) of said magnet valve, said closing elementand said armature are retained by a restoring spring (43) in a closedposition of said closing element on a valve seat (29) formed in saidintake line (10) from which the intake line (10, 31, 32, 33) leads tosaid pump work chamber (6), and said closing element is acted upon inthe closing position by a pressure prevailing in the intake line towardthe valve seat, said closing element includes a bore (50) which connectsa portion of said intake line (10) to parts of the intake line towardsaid pump work chamber which bore is closable by a valve member (61)acted upon by a closing spring (57) counter to the pressure in theportion of the intake line toward the pump work chamber, said closingspring (57) is supported in the armature (42) and said restoring spring(43) is supported in a stationary manner at one end.
 2. A magnet valveas defined by claim 1, in which the bore (50) in the closing element(28) is an axial bore, which discharges into a receiving bore (53) via aconical or spherical valve seat (52) and the valve member (61) and theclosing spring (57) are disposed in said bore (53).
 3. A magnet valve asdefined by claim 2, in which the receiving bore (53) passes axiallythrough the closing element (28) and the armature (42) and has a firmlyinserted intermediate spring plate (55), which serves as a support pointfor the restoring spring supported on the stationary core (41) of themagnet of the magnet valve, and serves as a support point for theclosing spring (57).
 4. A magnet valve as defined by claim 3, in whichthe valve member (61) is a ball, which is supported on a recess (60) ina spring plate (58) and which includes a tang (63) that is guided by amiddle opening (64) of the intermediate spring plate (55).
 5. A magnetvalve as defined by claim 4, in which the spring plate is made ofplastic.
 6. A magnet valve as defined by claim 3, in which theintermediate spring plate (55) is pressed into the receiving bore (53),which communicates with the intake line (10) via a transverse opening(66).
 7. A magnet valve as defined by claim 4, in which the intermediatespring plate (55) is pressed into the receiving bore (53), whichcommunicates with the intake line (10) via a transverse opening (66). 8.A magnet valve as defined by claim 5, in which the intermediate springplate (55) is pressed into the receiving bore (53), which communicateswith the intake line (10) via a transverse opening (66).